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What's the secret/trick to skim coating panels

36K views 126 replies 19 participants last post by  deadbodyman 
#1 ·
What are the tricks/methods to properly skim coat panels? I've skim coated my entire hood with Marson Platinum using a 5" spreader (or maybe it's a 6"), beginning at the center of the hood and spreading to the edge of the hood so I'm moving perpendicular to waves. I have maybe a half inch of overlap, or maybe an inch by the time I work it a little bit and try to blend them together and smooth them out.

I then go over it with 40 grit DA to knock down heavy stuff like ridges, etc. Then hit it with 80 grit DA to remove some of the body.

I guidecoat then block with my 16" durablock board with 220. It works well with the Platinum because it sands easy, and I don't have any adhesive rolls for lower grit and it helps me from taking too much off. I guidecoat again then block again.

I still feel waves even though metal is beginning to poke through in some places and I'm sure these are probably resulting from where I began a new spread.

:confused: Could use a little help here! What are your methods? Thanks.
 
#2 ·
Here is an article on the subject. Click here for the "Basics of Basics" Large flat panel repair.

Tech69 recently posted a thread with some tips as well. Click here for Henry's thread.

If you read the article basically what the biggest problem is on something like this is the panel flexes when you sand it. You may be blocking it "flat" but the panel is flexing flat while you are applying pressure, when you aren't pushing it flat, it isn't flat anymore!

Read the article and watch Henry's video and see if something doesn't spark.

Brian
 
#4 ·
skip99 said:
if i'm going to do a whole panel, i use spray poly...slick sand. etc. and you really need to use coarse paper to get it straight first..
Ahhh yes Skip that is the trick, cut it flat with some NEW, QUALITY, COARSE, paper so it CUTS the filler flat instead of "polishing" it.

Brian
 
#5 ·
Brian, I've read those articles before...I'm not using much down pressure so as to push down on the panel. These are narrow low spots anyways, ones that couldn't be created from pushing down on the panel.

I'm using new sandpaper, but of course as you can see it's not a very course grit for blocking. What grit are you using to cut it down?

I've read Henry's thread before too. The hood is actually laying flat on a large rolling table that's actually the same size as the hood so I don't have any parts of the saw horse stand pushing up on the skin anywhere.
 
#6 ·
skip99 said:
if i'm going to do a whole panel, i use spray poly...slick sand. etc. and you really need to use coarse paper to get it straight first..
How does this do for building? Do you still have to do some initial filler work too? I was watching some videos of some spray poly and they already had all the filler work done on the car first.
 
#8 ·
Lizer said:
Brian, I've read those articles before...I'm not using much down pressure so as to push down on the panel. These are narrow low spots anyways, ones that couldn't be created from pushing down on the panel.
ANY pressure can do this. I am talking it can be so touchy that you literally have to hold the sander so even it's own weight isn't on the hood as you run the sander over it. This sounds goofy but it's true, you literally need to "fly" the sander over the roof tops without landing. This is where NEW, QUALITY, SHARP, COARSE paper is so important.



Lizer said:
I'm using new sandpaper, but of course as you can see it's not a very course grit for blocking. What grit are you using to cut it down?
I am a big believer in CUTTING the filler flat. For this you need the coarsest paper possible for each step. Cutting that filler FLAT on a flexing hood, 40 grit if you must, heck 36 if you must. Now I don't use anything coarser than 80 anymore after some study of the subject back a while ago involving chatting with the Evercoat Tech line. But on a flexing hood, darn yes 40 is going to be used.

The polyester primer will fill a LOT and possibly all you need, it's hard to say being we can feel your hood. But realistically you are going to likely need some "bondo" first. This is where that 40 grit NEW, SHARP, QUALITY paper comes in, and CHANGED OFTEN. We are talking changing so often that you put the "used" paper back in the box for the next job where the panel isn't flexing. You hardly use it at all, and change it, why not? The SHARPER, NEWER, QUALITY paper you use the better, the more it will CUT without flexing the panel.

Personally I treat the polyester primer the same as polyester putty skim coat. I ONLY use it when I KNOW, I KNOW that it will be the last application.

I use it once I KNOW everything is filled and it's FLAT, I use it as a skim coat over the entire area to fill tiny imperfections and pin holes and sand scratches. At that point I am not trying to cut it FLAT, that has already been done with the COARSE, SHARP, NEW, QUALITY paper, it is FLAT but full of scratches too coarse for primer, like those 40 grit scratches. So polyester primer is applied over that to fill them.When sanding the polyester primer I go to 120 and even 180 but 120 scratches are pushing it, but quality urethane primer will handle them if you don't bomb the primer on and let it flash well between coats.

I can't emphasize enough that when using filler on the rest of the car where the panels aren't flexing you use finer paper and never ask the primer to fill so much, you don't need these coarse papers so much at all. But on that flexing hood, you need to go way overboard with paper, and lack of pressure so the paper does the cutting, and for this you need a coarser grit.

Brian
 
#9 ·
jamesl002 said:
I have maybe a half inch of overlap, or maybe an inch by the time I work it a little bit and try to blend them together and smooth them out.
Ignore jamesL002 post. It is a new style of troll I guess where they copy a line from a previous post and post it as their own. If you click on his name then "find post's by jamesl002" you will see that every post he has made is one of these copy and paste posts. Yes, bizarre but we all have our thing in life I guess.

Brian
 
#10 ·
Thanks so much Brian. That helps a lot. I've been bummed all day today because I was so disappointed and frustrated yesterday. Women have life to make them emotional; men have their cars! I am not going to touch this hood until I pick up a roll of some good...80 grit it sounds like. I do have sheets of 3M automotive 80 grit but it's not adhesive backed :(

I'm going to have to skim a fiberglass hoodscoop to go on it too; you can feel every place there's a structural casting on the underside. I would assume I will cut this exactly the same way then?

Also, do you have a recommendation for a spray poly?
 
#11 ·
Brian is giving you good advice here but one thing concerns me. You indicated you were using a DA for the initial blocking. If this is a fairly flat panel a DA is not adequate. Use a long firm sanding block or air file and sand in a sideways crosshatch pattern as you see in the videos. Best of luck.

John L
 
#12 ·
Lizer said:
Thanks so much Brian. That helps a lot. I've been bummed all day today because I was so disappointed and frustrated yesterday. Women have life to make them emotional; men have their cars! I am not going to touch this hood until I pick up a roll of some good...80 grit it sounds like. I do have sheets of 3M automotive 80 grit but it's not adhesive backed :(

I'm going to have to skim a fiberglass hoodscoop to go on it too; you can feel every place there's a structural casting on the underside. I would assume I will cut this exactly the same way then?

Also, do you have a recommendation for a spray poly?
I have had very good luck with Slick Sand from Evercoat.

Brian
 
#13 ·
John long said:
Brian is giving you good advice here but one thing concerns me. You indicated you were using a DA for the initial blocking. If this is a fairly flat panel a DA is not adequate. Use a long firm sanding block or air file and sand in a sideways crosshatch pattern as you see in the videos. Best of luck.

John L
I don't use the DA for blocking, just for knocking down the big stuff like the ridges left behind from the spreader and to remove obvious areas where the filler is piled higher. Once that stuff is taken off, then I guide coat and use my Durablocks. I do always block in a cross hatch pattern. Thanks.
 
#15 ·
Is there a benefit to Slick Sand over Featherfill?

I think I"m going to pick me up some surfacer so I can try it. Since we're on that topic, I skimmed the majority of the roof with Platinum and then blocked much of it back off, using guidecoat. My guidecoat was coming off pretty well and I thought I had it so I threw 3 coats of SPI 2k down on that and blocked it. You already know by now what happened, and that's lots of low spots...one so bad that I could really feel it under my hand; I don't know how I EVER missed that one in the first place because I use my hands so much when blocking. Anyways, I had initially shot the roof with 2 coats epoxy, then I'm sure I had put 3 coats of 2k over that and blocked it down before deciding I was going to need to skim....but don't remember for certain.

I'm wondering if a sprayable poly is an option but my concern is that I'll be building too much on the roof and end up with spider webbing in the finish some day...

If only I knew Brian's advice then. I've always blocked these open flimsy panels lightly but it was never the feather touch Brian was describing. Nor was I ever cutting to the degree he was describing either.
 
#16 ·
I did go to Evercoats web sight after Brian made his post. They list the Featherfill as a high build polyester and the Slick Sand as an extra high build polyester. I am looking forward to trying it.

Back in the 70's the first polyester primer I ever heard of was a brand called Eliminater. I painted my 47 Ford conv with it. Shot the car with S/W acrylic enamel with Polysol. Believe it or not that car is still around with that paint job still on it. The modern primers are unbelievably good.
 
#17 ·
Let's clarify something else here, exactly what kind of sander have you used? Because a "DA" like this, is a horrible tool for cutting filler of any kind. I still have a couple as they are THE tool for metal finishing (using no bondo in a repair) as I was taught many years ago. It's my tool of choice for door skins and the like.



But an ORBITAL sander like this is perfectly fine for roughing the panel into shape, it is effectively a "round block".



And the larger version a National Detroit 800 is my work horse, I am sorry, but after years of using this tool getting a panel long board flat isn't a dream, it's reality.



And this baby, a Hutchens 3800 is pretty hard to beat, an orbital long board.



Cutting filler with that NEW, SHARP, QUALITY paper on one of these tools is pretty hard to beat. You can hold it off the surface and apply as much or as little pressure as you want.

They are damn nice to have in the tool box. :D

Brian
 
#18 ·
Brian, I have an electric DeWalt orbit sander, approx 5". My compressor is only 3.7 hp/60 gallon, 13 CFM and can't keep up with an air hog DA. I have a cheap $40 DA that is absolutely worthless to me because I never use it. I've read on here you really need a good one.

Anyways, my electric orbit sander is slower but it's good for someone like me so you don't take too much off to fast. I've found it works really well initially as a round flat board as you described. When I'm doing my initial 40 grit rough in, then 80 grit rough in it will practically circle, then highlight, then point an arrow to and plant a little flag in all the low spots. Needless to say I know where they are before I ever start blocking or guide coat. Then I move on to my Durablocks.

ALWAYS another tool you need!
 
#19 ·
I will have to agree completely with Brian as to the importance of the initial cut of the filler has to be with a fresh course grit paper on a nice firm board sanding block, 36 grit on a 17 1/2 clip style longboard. If that is not flat from the start you will never get it flat with the finer grit papers on flexible blocks, esepecially on a big hood.
 
#20 ·
We all do things different, but you know what, I have never owned a flexible block. When all those mile long blocks came around, I never bought one, never saw a need. Now I am a tool nut and have bought many tools that I hardly use, I buy the best, (mostly) nothing but the best profesional tools. And I don't own any of those super long blocks or flexable ones.

I have done a ton of vintage cars and VW bugs, tons of them and never used one of those blocks getting those small curved panels like a Bug fender to the large panels like a hood on a mid sixties Chevy with zero waves or funks without any of those blocks. I look at the VW bug or 50 Chevy pickup fender as a "curved flat" if that makes any sense. I see no difference in blocking out a high spot in a flat panel or blocking out a high spot in a curved panel. You have a high spot you feel, you block it out so it's gone, never saw a need to think any different.

Brian
 
#23 ·
I tell you what, sometimes that fun gets long lost in times like these. I've been working on this body for three years now. I'm slow, deliberate, and perfectionist. I had taken some body classes for fun and became good friends with the instructor. He'd come out and help me on my car time to time and was floored when he saw some of my work; he thought it was The shop in town that did it (his former employer). Things like that are nice to hear, but I'd have been afraid to tell him how much time I had in that. Fortunately being an instructor he also wasn't shy to point out my flaws as that's really where I learn the most. I just want to be able to drive this thing before I die...

I'll be back either really happy or super pissed...we'll see :welcome:
 
#26 ·
Hey Josh, just looked at your blog. That is a well done site. Thanks for the link. You will get there. You showed a picture of the aftermarket rear valance not fitting quite right. I believe the lower edge (corner area) could be stretched gently which would let the panel settle in and close that gap. Do you know anyone who could help you with that? Maybe the instructor you were working with. The best of the replacement panels are what we call "near fit" panels. They are never completely correct. Hope I'm not getting to big for my britches but you obviously want this project to be the best it can be. Keep up the hard work.

John L
 
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